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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
Technical Design of the National Disposal Facility at Radiana in Bulgaria – 14291
E. Biurrun*, , E. Gonzalez Herranz**, T. v. Berlepsch*
*DBE TECHNOLOGY GmbH, Eschenstr. 55, D-31224 Peine, Germany
[email protected]; [email protected]
**Westinghouse Electric Spain SAR, Padilla 17, E-28006 Madrid, Spain
[email protected]; [email protected]
ABSTRACT
In October 2011 a Consortium composed by Westinghouse Electric Spain SAU, ENRESA and
DBE Technology GmbH was awarded by SERAW with a contract for the design of the Bulgarian
low and intermediate level waste repository. The facility will consist of 66 reinforced concrete cells
capable of receiving 18,600 conditioned waste containers during 60 years, and the related
auxiliary facilities and buildings.
After a comprehensive study of the documentation, SERAW approved the recommended
Conceptual Design on December 2012, and authorized the Consortium to start developing the
Technical Design. The complete package of the Technical Design documentation prepared by the
Consortium consists of 19 separate chapters and fills around 50 folders with approximately 6500
pages. As the general progress of the project lies within the planned deadlines, it is reasonable to
assume that a license for construction of the NDF can be expected in the course of 2014.
INTRODUCTION
In the framework of the accession treaty to the European Union the Republic of Bulgaria
committed itself to the early decommissioning of the four WWER 440-V230 reactors of the
Kozloduy Nuclear Power Plant (KNPP). Due to this early decommissioning large amounts of low
and intermediate radioactive waste will arise much earlier than initially scheduled. In order to
manage the radioactive waste from the early decommissioning, Bulgaria has intensified its efforts
to provide a near surface disposal facility for low and intermediate level waste at Radiana with the
required capacity. It is supported in this endeavour by a compensation mechanisms established
by the European Union, the “Kozloduy International Decommissioning Support Fund (KIDSF)”,
aimed at alleviating the significant impact of the early NPP phase out on Bulgaria`s economy. The
fund is managed on behalf of the European Union by the European Bank for Reconstruction and
Development (EBRD).
In a series of projects the State Enterprise for Radioactive Waste (SERAW) selected a site for the
National Disposal Facility (NDF) at Radiana in the vicinity of the KNPP and also specified
Enresa’s facility at El Cabril as reference design for the NDF. 2011 a further project was launched
and assigned in international competition to a consortium of DBE TECHNOLOGY (Germany),
Enresa and Westinghouse (both Spain) to provide the complete technical planning including the
preparation of the Intermediate Safety Assessment Report.
The NDF design work started in October 2011, initially focusing on the repository Conceptual
Design. After a comprehensive study of the documentation, SERAW approved the recommended
Conceptual Design on December 2012, and authorised the Consortium to start developing the
Technical Design. Meanwhile the Technical Design work has been completed and submitted to
SERAW for review and analysis. Simultaneously to the preparation of the Technical Design for
the NDF, the consortium is working on the Intermediate Safety Analysis Report (ISAR). This key
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
document is intended to provide convincing proof that the NDF, constructed and operated in line
with all requirements of the Technical design, and filled with waste packages in compliance with
the Waste Acceptance Criteria prescribed in the ISAR, will be safe according to the present
state-of-the-art for a near surface repository.
DEVELOPMENT OF THE TECHNICAL DESIGN
Due to the tight project schedule the development of the Technical Design started even before
final approval of the Conceptual Design in December 2012. Some requirements could only be
finally defined during the development of the Technical Design (e. g. requirements on the design
for physical protection of the NDF) and requirements from a number of authorities have to be
complied with. Despite the challenging schedule for the project, the general progress lies within
the planned deadlines because of the constructive cooperation between SERAW and the
consortium. Hence, it is reasonable to assume that a license for construction of the NDF can be
expected in the course of 2014.
In order to assure sufficient quality in the development and review of the Technical Design the
document has been structured following Bulgarian requirements for investment projects into 19
separate design parts as listed below. Additionally, in each design part of the Technical Design
the documentation, which corresponds to the respective buildings and facilities in the General
Layout Plan (GPL), is arranged in up to 23 separate sub-parts. The use of sub-parts is optional,
i. e. they are only considered if necessary. For example, is the design part Architecture
subdivided into 19 subparts describing in detail the fundamental connections and parameters of
the premises and the common areas, while there is only one subpart for the Design Part Geodesy
providing the topographical base for the project. In total the Technical Design documentation
prepared by the Consortium fills around 50 folders with approximately 6500 pages.
Design Part
Description
General
essential aspects of the design of the NDF
General Layout Plan
basic principles, design parameters and interconnection of
the premises and the common areas
Geodesy
topographical base for the project
Roads
conditions for traffic and parking of the motor vehicles, for
maneuvering of the fire safety vehicles and for pedestrian
movement
Technology
technological process for acceptance of radioactive waste
packages into the site, its emplacement in the disposal cells,
the circulation of vehicles and people for the operation in the
Facility
Architecture
fundamental connections and parameters of the premises
and the common areas
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
Building Structures
general description of the buildings and structures
Power Supply and Electrical
Systems
electrical systems of the NDF, their structure and des-cription
Control and Management
Systems. Radiation
Monitoring
structure of the control and management system, and its
design basis and description; overall basic plant control and
super-vision system is presented
Water Supply and Sewerage
external and building water supply systems, the sewerage
and the rainwater collection pond
Heating, Ventilation and
Air-conditioning (HVAC)
technical solutions for conditioning the air in the auxiliary
buildings
Energy Efficiency
Demonstration of compliance with energy efficiency
requirements
Fire Protection
main functions, design criteria and the technical solutions for
the NDF Fire Protection System
Physical Protection
Physical Protection System aimed to prevent, detect and
impede malvalicious acts
Health and Safety Plan
Demonstration of compliance with requirements for health
and safety at work during construction and installation
activities
Organization and Execution of NDF construction activities and their sequence
Construction
Cost Estimate Documentation
Cost estimation reflecting the technical solutions
Table 1: Design Parts of the Technical Design
DESIGN BASIS
The Radiana site, with a surface area of approximately 46 hectares, has quasi-rectangular shape
with maximum dimensions of 470 m x 1250 m., It is adjacent to the Kozloduy NPP, located
between two roads, one on the north controlled by the NPP and considered as an interplant road
which connects the town of Kozloduy with the NPP, and one on the south, a secondary road.
Geographically speaking the site is located between the second and sixth loess terraces in the
non-flooded right bank of the river Danube.
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Fig. 1: General Site Location
The NDF shall be able to accept and dispose of all radioactive waste (RAW) of category 2a arising
in Bulgaria from the operation and dismantling of the national nuclear facilities. From a more
generic viewpoint, the "Category 2a" waste corresponds to what is usually denominated as
Short-Lived, Low and Intermediate-Level Waste (SL-LILRW). According to present forecasts the
NDF will receive conditioned waste packed in 18,615 cubic-shaped concrete containers (i.e.,
waste packages). The waste packages have a side length of 1.95 m and a weight of 20 tones. The
total volume occupied by these waste packages will be 138,200 m3. The radionuclide inventory
will be determined more precisely in the framework of the ISAR, but was preliminarily expected to
be approximately 2.4 × 1014 Bq.
Long-term waste isolation is best achieved by a multiple barriers isolation system. In such a
system the hazardous radionuclides contained in the waste are confined in containment
structures consisting of several barriers acting in series. The isolation function is guaranteed by
the system as a whole so that possible deficiencies of a barrier or its degradation in the course of
time are compensated by the other barriers, thus ensuring that the protection objectives are
achieved. The NDF design relies on a multiple barrier isolation system.
The NDF multi-barrier system includes the following parts:
•
•
The first engineered barrier is the waste package, including the cement matrix, the
radioactive waste and the reinforced concrete cask. The safety function assigned to the
waste package is to ensure the full retention of radioactive waste by maintaining its
mechanical integrity throughout a period of at least 50 years.
The second engineered barrier of the repository includes the reinforced concrete walls of
the disposal cells, and the lower and upper slabs. The assigned safety function is the
retention of potential releases of radionuclides from waste packages, by maintaining
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
•
integrity through a period of 300 years to the extent reasonably achievable.
The third (external) engineered barrier includes the external loess-cement cushion and
the multilayer cover. Apart from being a barrier against the migration of radionuclides, the
loess-cement cushion also increase the thickness of the unsaturated zone and improve
the overall foundation conditions. The multilayer protective cover is constructed with
natural materials (clay, sand, gravel, etc.).
The safety of the facility is based on the defense-in-depth concept, which consists on the
simultaneous application of a system of physical barriers and administrative measures. The
design of the NDF is aimed to prevent:
•
•
•
Creation of conditions leading to a break in the integrity of physical barriers;
Failure of a physical barrier in the case of the above conditions;
Failure of a physical barrier as a result of failure of another physical barrier.
Radiological safety is of paramount importance in the repository facility. In line with the applicable
regulations any unavoidable exposure of the staff and the public must be kept as low as
reasonably achievable (ALARA). The design of the NDF ensures that it will keep its function and
that the dose limits will not be exceeded during normal. This is achieved by defining the necessary
design limits, operational states, safety classification of systems, structures and components
(SSCs) and important design assumptions.
All SSCs of the facility have been classified in line with their importance to the nuclear safety and
radiological protection of the NDF into Safety Class (SC) and Non-Safety Class (NSC).
Furthermore, they have been classified into the seismic categories 1 (C1) and 2 (C2) and the Non
Seismic Category (NC). Furthermore, all elements of the NDF have been classified in different
Quality Levels to be taken into account during the design, construction, operation and institutional
control of the facility. The proposed classification is consistent with the Safety and Seismic
Classifications and introduced some additional concepts such as the decision of SERAW about
important measures to ensure the quality of all activities in the NDF.
REPOSITORY CONCEPT
Repository Design
For practical and operational safety reasons the repository facilities have been grouped into a
1. Disposal zone, in which the disposal cells are located, and
2. A building zone, in which the Waste Reception and Buffer Storage (WRBS) Building, the
site administration, control room and ancillary and support buildings are located.
The general site layout is shown in Figure 2.
To ensure operational safety, and to optimize the protection of the public, it is necessary to
consider the effects of direct radiation from the waste packages. The establishment of
special-statutory areas around the facilities and building of the NDF takes care of this fact. It is
aimed at allow for appropriate radiation monitoring and limiting the exposure of the staff and of the
public to radiation during normal operations and in the event of design basis accidents.
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
Fig .2: Artistic View of NDF Site Layout
The areas, which are inside the outer fence of the NDF, are subdivided based on the following
criteria:
Radiation Protection area:
•
•
Regions where dose rate levels exceed 0.05 μSv/h. This figure results from considering a
dose limit of 0.1 mSv per year as the limit for persons with a presence of 2000 hours per
year in the area. This corresponds to the limit for non-radiation-exposed workers
(“collocated” workers).
Region where the consequences of the design basis accident may be above of 5 mSv.
Monitored area:
•
All the area inside the outermost fence and outside the above mentioned radiation
protection areas. The dose rate here is under 0.05 μSv/h.
The Radiation Protection areas of the facility are subdivided into areas according to their
radiological conditions, taking into account the external exposure risks that exist for workers
entering these areas, as follows:
•
•
Controlled Area: exposures could be higher than 6 mSv/year (3/10 fraction of the
exposure limit for workers)
Supervised Area: dose rates between 1 and 6 mSv/year (that corresponds to the limit for
category B workers)
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
A dose rate assessment is performed for each area considering the layout of the radiation
sources and shielding provisions. The criteria for granting access to the different areas is
established in line with the radiological protection limits.
The NDF has sixty-six (66) disposal cells (DC) for waste package disposal. These disposal cells
are located on three (3) equal platforms, each with twenty-two (22) disposal cells and their related
systems. A first disposal platform will be constructed prior to disposal start, the second one
approximately after 20 years, the third platform after 40 years of operation. The disposal cells are
arranged in two lanes, each with eleven disposal cells. The disposal cells are monolithic
rectangular boxes with two inner walls made of reinforced concrete, with a capacity for 288 waste
packages emplaced in 3 chambers of 96 waste packages each (8 × 3 waste packages in plan, 4
layers in height). The external dimensions of each disposal cell are 20.15 m long by 17.05 m wide.
The height is 9.45 m measured from the foundation level up to the top of a full and sealed disposal
cell. Each storage platform will host 6,336 waste packages corresponding to about 20 years of
repository operation. The total disposal capacity of the NDF will be 19,008 waste packages.
After a disposal cell is fully loaded with waste packages, it will be closed with a reinforced
concrete slab. During the disposal process and the construction of the concrete slab the cell will
remain covered by a mobile roof to protect the loading and closing operation works from weather
phenomena. The mobile roof also houses the bridge crane used to emplace the waste packages
into their position within the disposal cell.
A critical component of the disposal system is the Infiltration Control Network. It consists of a pipe
system to collect and control the water that could enter a disposal cell after its closure and interact
with the waste packages. The pipes are located in an underground gallery that runs below each
row of disposal cells; this gallery is accessible by personnel. The system includes a pipe
connection coming from each disposal cell and a collection tank. Water is exclusively driven by
gravity.
The Building Zone contains the entire infrastructure needed for the efficient and safe operation of
the NDF. The most important structure in this zone is the Waste Reception and Buffer Storage
(WRBS) Building located at the entrance of the NDF within the regulated and restrictive area. The
WRBS Building is designed to receive the transport vehicles loaded with a radioactive waste
package that arrive at the NDF. The waste package is unloaded in this building and the vehicle is
decontaminated (if needed) prior to departure. The radiological control of the waste packages
arriving at the NDF is performed also here. Another main function of this building is to provide a
buffer storage capacity of 120 waste packages that allows for the regulation and optimization of
the waste package flow to the disposal cells.
The NDF also includes the following auxiliary infrastructure necessary during the operational
phase:
•
•
•
•
•
Checkpoint – provides access control for personnel and transport vehicles to and from the
NDF site;
Administrative Building – provides suitable working conditions for the personnel of the
NDF;
Laboratories – provide equipment for carrying out laboratory analyses of samples from
contamination tests and environmental samples as required;
Auxiliary Buildings – the garage workshops with different purposes and an industrial
section which contains facilities for power equipment and other auxiliary systems;
General Services Building – Include access to the radiologically controlled zones and to
public relations services.
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
These facilities are in separate buildings all connected by a central corridor that also provides
access (through a radiological check point) to the WRBS Building.
Repository Operation
The NDF has a single main access that links the Kozloduy NPP road with the Building Zone, thus
providing the most direct access for the waste packages. The access of the waste packages to
the WRBS Building (restricted zone) is direct after passing the security and control zone, avoiding
the circulation near the administrative zone.
The waste package disposal operation begins in the WRBS Building waste package
loading/unloading area. Here an internal transport vehicle is loaded with a waste package. This
vehicle goes, always through the internal route in the radiologically controlled area, to the
assigned disposal cell and parks behind the mobile roof where the portal crane lifts the waste
package and hoists it to its storage position within the disposal cell.
Once the disposal cell is filled up with all the waste packages, the reinforced concrete slab is set in
place on the top. Before the mobile roof is displaced to the next disposal cell position, a watertight
membrane is set over the reinforced concrete surface of the disposal cell.
The process finalizes after the repository is full with the construction of a long-term cover made of
different materials arranged to prevent the intrusion of water into the disposal cells during the
surveillance phase.
Initially, the NDF will be able to accept up to 800 waste packages per year, i.e., four waste
packages per day. When all the waste currently stored in the interim storage facility adjacent to
the Kozloduy NPP has been disposed of, the NDF will work single shifts of 7 hours per day, 5 days
per week, about 200 days per year, allowing for down time due to severe weather conditions. The
disposal rate will then be only one waste package per working day.
PROJECT IMPLEMENTATION
A staggered construction approach has been adopted. The NDF will be built in three stages:
•
•
The auxiliary installations and the first platform of disposal cells will be built during the first
stage. This would provide a full compliant disposal facility, fulfilling all the requirements
and design criteria, but without the total number of disposal cells.
During the second and third stage the Facility will expand to come up to its full capacity
through the construction of the second and third platforms and their respective
infrastructure.
The design of the NDF considers the construction during the second and third stage
simultaneously with the operation of the auxiliary buildings and the first disposal cell platform.
Once the auxiliary buildings and the first disposal cell platform became operative, it will be
possible to proceed with the disposal of waste packages and the construction of the remaining
disposal cell platforms simultaneously. For that purpose a temporary road separate from the main
entrance will provide direct access to the construction area. This road will avoid interferences
between construction vehicles and the transportation of radioactive waste during operation.
The following main phases are envisaged for the NDF Life Cycle:
•
•
•
Operation: 60 years;
Closure phase after disposal end: 15 years;
Institutional control after closure: 300 years.
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WM2014 Conference, March 2 – 6, 2014, Phoenix, Arizona, USA
During the operation phase the waste packages are received and emplaced in the disposal cells.
Once a disposal cell is full, the disposal cell will be closed with the upper slab and a protective
coating.
In the closure phase the multi-layer cover will be built and the rest of buildings not necessary for
the further institutional control will be decommissioned.
During the institutional control period the surveillance of the site will be assured. The only work to
be performed will be eventual maintenance or repair interventions, if necessary. The activity
content of the NDF will be limited to permit the use of the site without radiological restrictions after
the institutional control phase (i.e., after 300 years post-closure).
OUTLOOK
In November 2013 the Technical Design has been approved by SERAW for submittal to the
licensing authorities. It is now expected that after a thorough review of the documents very soon
detailed technical discussions will commence. Nevertheless, due to the good cooperation
between SERAW and the consortium it is expected that generally all requirements are met.
Nevertheless, it is noteworthy that changes in the regulation this year require amendments of the
ISAR, in turn having consequences for the Technical Design. Even though the consequences are
expected to be very limited only a further revision will be unavoidable.
But it is still believed that that a license for construction of the NDF can be expected in the course
of 2014.
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